A lithium secondary battery is roughly classified into a cylindrical battery cell, a prismatic battery cell, a pouch type battery cell, and the like, depending on an exterior thereof, and is also classified into a lithium ion battery, a lithium ion polymer battery, a lithium polymer battery, and the like, depending on a form of an electrolyte thereof.
In accordance with the recent trend toward miniaturization of mobile devices, the demand for a prismatic battery and a pouch type battery cell having a thin thickness has increased. Particularly, a pouch type battery cell of which a shape may be easily changed, manufacturing cost is cheap, and a weight is small has been highly spotlighted.
In general, the pouch type battery cell indicates a battery in which an electrode assembly and an electrolyte are sealed in a pouch type case made of a laminate sheet including a resin layer and a metal layer.
Referring to FIG. 1, a battery cell 10 has a structure in which an electrode assembly 30 including a cathode, an anode, and a solid electrolyte coating separator disposed therebetween is sealed in a pouch type battery case 20 so that two electrode leads 40 and 41 electrically connected to cathode and anode tabs 31 and 32 of the electrode assembly 30 are exposed in parallel with each other.
The battery case 20 includes a case body 21 including a concave accommodation part 23 on which the electrode assembly 30 may be seated and a flat plate cover 22 integrally connected to the case body 21.
The battery case 20 is made of a laminate sheet, and includes an outer resin layer 20a forming an outermost portion, a blocking metal layer 20b preventing penetration of a material, and an inner resin layer 20c for sealing.
In the stack type electrode assembly 30, a plurality of cathode tabs 31 and a plurality of anode tabs 32 are each fused and bonded together to the electrode leads 40 and 41. Further, in order to prevent a short-circuit from occurring between a thermal bonding device and electrode leads 41 and 41 and secure sealing performance between the electrode leads 40 and 41 and the battery case 20 when an upper end portion 24 of the case body 21 and an upper end portion of the cover 22 are thermally bonded to each other by the thermal bonding device (not illustrated), an insulating film 50 is attached to upper and lower surfaces of the electrode leads 40 and 41.
Since the battery cell as described above generally has a planar structure, it is easy to stack a plurality of battery cells, and it is easy to bond leads to each other based on electrode leads having a protrusion structure. Therefore, a plurality of battery cells are stacked and connected to each other to thereby be used as a battery pack structure.
In relation to this, FIG. 2 is a schematic side view illustrating an example of a battery pack.
First, a battery cell 10 generally has a shape corresponding to an exterior of an electrode assembly 30. More specifically, based on a flat plate cover 22 of a battery case 20 forming an upper surface a of the battery cell 10, an accommodation part 23 is formed downwardly, the accommodation part 23 corresponding to a shape of the electrode assembly 30 and side surfaces of the battery cell 10 form a lower surface b, and a pair of electrode leads 40 and 41 protrude outwardly from the battery case in parallel with each other in a shape in which the electrode leads 40 and 41 and the flat plate cover form a straight line based on a cross section of the battery cell. The electrode leads are electrically connected to each other in a state in which a plurality of battery cells as described above are stacked upward based on the ground, thereby forming a single pack structure.
In a structure in which the battery cells are connected in series to each other as illustrated in FIG. 2, since electrode leads 41 and 40′ of the battery cells 10 and 10′ stacked in a state in which upper surfaces a and a′ of the battery cells 10 and 10′ face each other are adjacent to each other, it may be difficult to maintain an insulation state between the electrode leads 40′ and 41 that should not be connected to each other for configuring a serial circuit.
Therefore, a structure in which battery cells of which upper surfaces a and a′ face each other are spaced apart from each other to have an interval therebetween may be considered, but this structure may increase a volume of a battery pack 90.
Unlike this, in the case of additionally mounting a member 92 such as an insulating sheet or pad for preventing a contact between the electrode leads 40′ and 41, a cost may be increased and a mounting process may be added, such that an entire manufacturing process may be complicated.
Further, even in the case of changing structures of some of the battery cells for insulation, equipment for manufacturing the battery cell having the changed structure should be additionally added, which is inefficient in view of manufacturing process.
Therefore, there is a high need for a battery cell having a structure with high insulation reliability of electrode leads while being standardized in a range in which manufacturing processability is not inhibited, and a battery pack including the same.